The Dow Jones Industrial Average (DJIA) and the Standard \& Poor's 500 Index (S\&P 500$)$ .
are both used to measure the performance of the stock market. The DJIA is based on the price of stocks for 30 large companies; the S\&P 500 is based on the price of stocks for 5000
companies. If both the DJIA and S\&P 500 measure the performance of the stock market, how are they correlated? The following data show the daily percent increase or daily
percent decrease in the DJIA and S\&P 500 for a sample of nine days over a three-month period (The Wall Street Journal, January 15 to March $10,2006 )$
a. Show a scatter diagram.
b. Compute the sample correlation coefficient for these data.
c. Discuss the association between the DJIA and S\&P 500. Do you need to check both
before having a general idea about the daily stock market performance?